Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 01/18/94

Final Date: 05/31/94

Deleted Date:

The eight-acre Frontier Fertilizer Superfund Site (Site) is located near the eastern city limit boundary line in the City of Davis, California. The Barber and Rowland Company operated a pesticide and fertilizer distribution facility on the Site from 1972 to 1982. The Frontier Fertilizer Company used the Site from 1982 to 1987. Both companies handled chemicals on the western four acres of the Site. Operations consisted of storing, mixing and delivering pesticides, herbicides, and non-bulk chemicals in cans, drums, and other containers. Both companies used a 4,000-cubic-foot former disposal basin in the northwest corner of the site to dispose of unused pesticides and fertilizers. Returned tanks and containers were washed and the rinsate was dumped into the disposal basin or onto the ground. In 1985, Frontier Fertilizer excavated approximately 1,100 cubic yards of contaminated soil from the former disposal basin and land farmed the soil on a field east of the Site. In 2000, all structures, above-ground tanks, and underground tanks were removed with the exception of a warehouse which contains the groundwater treatment system. The Mace Ranch residential subdivision is approximately 800 feet north of the Site. The field immediately north of the Frontier Site is planned for development as the Mace Ranch Light Industrial/Business Park. Development in this area began in the Summer 2003 with completion of two sections of Faraday Road and below-ground utilities.

There are four water-bearing zones beneath the Frontier Site, which are generally separated by layers of clay. The first encountered shallow water bearing zone, called the S-1, extends from approximately 30 to 50 feet below ground surface (bgs). Below the S-1 is a second shallow water bearing zone, called the S-2, which extends from approximately 60 to 90 feet bgs. The S-1 and S-2 zones are not currently used as sources of drinking water. The third water bearing zone, the A-1 aquifer, extends from approximately 110 to 130 feet bgs; however, the drinking water supply for the City of Davis comes from the deep, fourth encountered water bearing zone, the A-2 aquifer, which begins at approximately 180 feet bgs. No Site contaminants above drinking water standards have been detected in the A-2. Groundwater flow direction is to the north- northeast in the S-1 and S-2 zones, while groundwater flow direction in the A-1 aquifer is generally to the southeast. Contaminated groundwater has migrated north of the Site beneath the Mace Ranch subdivision.

Although contamination from the Frontier Site has not been documented in any drinking water wells, the potential for contamination migration from the Frontier Fertilizer Site exists in areas where the water-bearing zones are hydrogeologically connected.

Contaminants and Risks

Contaminated Media

Groundwater

Soil and Sludges

The principal chemicals in groundwater are four pesticides, ethylene dibromide (EDB), 1,2-dichloropropane (DCP), 1,2,3-trichloropropane (TCP), and 1,2-dibromo-3-chloropropane (DBCP), which were used as soil fumigants, as well as the solvent carbon tetrachloride. Nitrate has also been detected in groundwater above drinking water standards.

Groundwater in the S-1, S-2 and A-1 zones is contaminated with the above chemicals. The A-2 aquifer, which is the drinking water supply for the City of Davis, is not contaminated.

Who is Involved

Investigation and Cleanup Activities

EPA's goals are to halt the migration of contaminated groundwater, to restore the affected groundwater to drinking water quality standards, and to remediate contaminated soil in the former waste pit area, so that it no longer acts as an ongoing source of contamination to groundwater.

Initial Actions

The California Department of Toxic Substances Control installed a small groundwater extraction and treatment system in early 1993. EPA installed a larger system in 1995. The system was upgraded in Fall 2000 and again in 2002. The groundwater extraction wells for the existing system are in the field immediately north of the Site. EPA has also installed groundwater monitoring wells on-site, in the field immediately north of the Site, and in the Mace Ranch residential subdivision. EPA collects and analyzes water samples for chemical contaminants and measures water levels in these wells on a quarterly, semi-annual, or annual basis, depending on the location of the well.

Site Studies

EPA collected samples of groundwater and surface and subsurface soils to determine the nature and extent of contamination and reported the results in an April 1997 Remedial Investigation (RI) Report. The studies reported that soil contamination was confined to the waste disposal basin area, and that contaminated groundwater existed in the upper three water-bearing zones and had migrated off-site. A June 1999 Supplemental Remedial Investigation Report described sampling results from groundwater monitoring wells in the Mace Ranch Park subdivision as well as soil gas sampling results. Soil gas samples were collected on top of the former waste disposal basin and at 50 foot intervals to the Mace Ranch Park subdivision. Groundwater sampling data indicted much higher levels of contamination on-site and immediately north of the Site, compared with those sampling data collected from Mace Ranch Park. Similarly, soil gas chemical contaminant concentrations were higher on-site and decreased rapidly at sample locations just north of the Site.

A Baseline Risk Assessment was produced in April 1999. An indoor air risk assessment for the residents of Mace Ranch was included in the Baseline Risk Assessment. The indoor air risk assessment determined that there is no risk to residents of Mace Ranch from volatile chemicals in groundwater moving up through soil and into homes.

In Fall/Winter 2001 and Spring 2002, EPA collected additional groundwater samples in the Mace Ranch subdivision and collected soil, soil gas and groundwater samples on-site and in the field immediately north of the Site to better define the geology and extent of groundwater contamination. A groundwater extraction well cluster was installed at the intersection of Caricia Drive and Arroyo Avenue and in the field immediately north of the former disposal basin. A new groundwater monitoring well cluster was installed on Fifth Street near Entrada.

The groundwater sampling results show elevated concentrations in the S-1 and S-2 zones on-site and immediately north of the Site. These concentrations generally decrease sharply within a few hundred feet from the former disposal basin, although a localized area of groundwater with elevated pesticide concentrations was found in the S-2 zone near the intersection of Caricia and Arroyo in Mace Ranch Park.

Soil gas data indicted chemical concentrations lower than those observed in samples collected in 1997, indicating that the risk calculations performed using data from the earlier sampling for the 1999 Baseline Risk Assessment, which were found to be protective, were still germane. Soil sampling identified a zone of soil contamination extending from near the ground surface down to about 30 feet bgs in the area next to the former disposal basin. Soil samples collected about 60 feet north of the disposal basin indicated contamination about 30 to 80 feet bgs, although at much lower concentrations than the shallow soil contamination near the former disposal basin. The results of this field work are described in Supplement No. 2 to the Remedial Investigation Report, dated January 2003.

Remedy Selected

In June 2006, EPA finalized a Feasibility Study (FS) that includes a detailed analysis of alternatives for final clean-up of on-site contaminated soils and groundwater. EPA issued a Proposed Plan on June 12, 2006, that recommended clean-up alternatives for soil and groundwater. As part of a formal 30-day review process of the Proposed Plan, EPA held a public meeting on June 22, 2006, to discuss the proposed clean-up alternatives and record verbal comments.

The Record of Decision (ROD) for the site was signed on September 28, 2006. The major remedial components described in the ROD include: the use of electrical energy to heat the most contaminated area of the Site (in order to transform the contaminants to a less toxic state); to continue using the existing groundwater extraction and treatment system; to investigate secondary anaerobic bioremediation for possible nitrate treatment; and, restrict access to the Site and cap soil areas where there is contamination until the property is developed.

Remedy Design

EPA finished the heating treatment system design in the fall of 2009. System installation began in the winter of 2010 and operation (heating) started in February 2011.

Cleanup Results to Date

As described above, EPA has been operating a groundwater extraction and treatment system since 1995. While the system has been effective in removing contaminants from groundwater in the field north of the Site, quarterly groundwater monitoring data shows that the system is not capturing all of the plume (the area of contaminated groundwater) in the Mace Ranch subdivision. EPA expanded the groundwater extraction and treatment system starting in August 2003 to further enhance the plant effectiveness. Expansion included installation of five new wells capable of extracting and monitoring contaminated groundwater, completion of four extraction wells and replacement of pressurized treatment system discharge plumbing with a gravity flow line to facilitate increased pumping capacity and reduced energy demand. Groundwater extraction and plant optimization is on-going.

Community Involvement

Public Meetings: Fact Sheets are planned to present progress.

- Community Update Meetingswere held on January 18, 2011 and October 12, 2011 to discuss the “Heating System” start up and answer questions from the community.
- Community Update Meeting was held October 28, 2009 to present design for in-place heating.
- Proposed Plan Public Meeting was held on June 22, 2006.